In known embodiments of the above joints, such as the one shown schematically in cross section in FIG. 1 of the accompanying drawings, plate 1 which reinforces the flexible strip 2 is flat and horizontal and so are the heels 3 of frames 4.
In this case, the mutual movements drawing the frames towards each other, shown symbolically by arrows F, and due to expansion of slabs 5 on which these frames rest, which movements tend to close gap 6 separating said slabs, result in plate 1 being raised as shown by arrow X and conversely.
These vertical movements of the median zone of the joint are only tolerable if their amplitude is small.
In practice, it is considered that the level of said median zone of the joint should not exceed by more than 2 mm the average level of the upper faces of the two slabs 5 so that a vehicle travelling rapidly over the joint does not cause unpleasant jolting of said vehicle. Now, in practice, when it is very hot and when the width of gap 6 is at a minimum, the difference in level may reach or even exceed 5 mm.